The in-plane lattice constants of bulk STO (111) and NbN (111) are 0.552 nm and 0.310 nm, respectively. 1(c) is nearly equal to that from the NbN film in Fig. The separation of the streaks from the STO substrate in Fig. The incident electron beam is along the STO direction of the STO substrate. Both of them give sharp streaky 1 × 1 RHEED patterns. The homogeneous spatial distribution of superconducting gaps and magnetic vortices further demonstrates the high quality of the NbN films prepared by PAMBE.įigures 1(a) and 1(b), respectively, show the surface morphology of the initial STO (111) surface and the NbN (111) film with a thickness of 20 nm. Furthermore, the superconductivity of the NbN (111) films is studied by low-temperature scanning tunneling spectroscopy (STS). For the annealing temperature above 800 ☌, loss of nitrogen leads to a 2 × 2 surface reconstruction. Moreover, we find that the terraces of the as-grown NbN (111) films become wider as the increase of the annealing temperature in ultrahigh vacuum. As the substrate temperature is increased above 700 ☌, atomically flat NbN (111) films with single orientation can be prepared. When the substrate temperature is lower than 700 ☌, the NbN (111) films consist of small islands on STO. Using scanning tunneling microscopy (STM) and in situ reflection high energy electron diffraction (RHEED), we investigate the surface morphology of NbN (111) films. By optimizing the substrate temperature, the NbN (111) films can be prepared under the N-rich condition. Nb-doped SrTiO 3 (111) (STO) is used as the substrate due to its small lattice mismatch with NbN (111) (∼2.8%). In this work, we report atomically flat NbN films grown by PAMBE.
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